U.S. patent application number 10/036373 was filed with the patent office on 2002-09-05 for ground detection apparatus for electric vehicle.
This patent application is currently assigned to Nissan Motor Co., Ltd.. Invention is credited to Suzuki, Kouhei.
Application Number | 20020121902 10/036373 |
Document ID | / |
Family ID | 18872351 |
Filed Date | 2002-09-05 |
United States Patent
Application |
20020121902 |
Kind Code |
A1 |
Suzuki, Kouhei |
September 5, 2002 |
Ground detection apparatus for electric vehicle
Abstract
A ground detection apparatus for electric automobile having a
high-voltage DC power supply (31) which is electrically insulated
from a body and a three-phase AC motor (33) which is driven by a DC
voltage from the high-voltage DC power supply. A ground detection
signal consisting of a square waveform is supplied to the DC power
supply circuit through a detection resistor and a coupling
capacitor, a voltage amplitude of a ground detection point serving
as a connection point between the detection resistor (3) and the
coupling capacitor (4) is detected, the detected voltage amplitude
is converted into an insulation resistance on the basis of the
relationship between a preset voltage amplitude and a preset
insulation resistance, and levels of insulation resistance
deterioration of the high-voltage DC power supply are detected by
comparing the converted insulation resistance with a preset ground
decision threshold value.
Inventors: |
Suzuki, Kouhei; (Tokyo,
JP) |
Correspondence
Address: |
McDERMOTT, WILL & EMERY
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
Nissan Motor Co., Ltd.
|
Family ID: |
18872351 |
Appl. No.: |
10/036373 |
Filed: |
January 7, 2002 |
Current U.S.
Class: |
324/509 |
Current CPC
Class: |
G01R 31/34 20130101;
G01R 31/1227 20130101; B60L 3/0023 20130101; B60W 2050/143
20130101; G01R 31/007 20130101; B60L 3/0069 20130101; B60L 2200/26
20130101; G01R 27/18 20130101; G01R 31/52 20200101 |
Class at
Publication: |
324/509 |
International
Class: |
G01R 031/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 2001 |
JP |
P2001-004120 |
Claims
What is claimed is:
1. A ground detection apparatus for electric vehicle having a DC
power supply circuit which is electrically insulated from a body of
vehicle, comprising: a coupling capacitor which is connected to the
DC power supply circuit; a detection signal generator outputting a
ground detection signal comprising a periodical waveform, the
detection signal generator being connected to one terminal of the
coupling capacitor through a detection resistor; a signal detector
detecting a voltage amplitude of one terminal of the coupling
capacitor; a converter converting the detected voltage amplitude
into an insulation resistance on the basis of the relationship
between a preset voltage amplitude and a preset insulation
resistance; and a level detector detecting levels of insulation
resistance deterioration of the DC power supply circuit by
comparing the converted insulation resistance with a preset ground
decision threshold value.
2. An apparatus according to claim 1, wherein the signal detector
performs sampling of the voltage amplitude at a predetermined
period.
3. An apparatus according to claim 1, wherein: the signal detector
performs sampling of the voltage at a sampling period which is a
half the period of the periodical waveform to detect the voltage;
and a calculator calculates a difference between a first voltage
detected by the odd-numbered sampling at the sampling period and a
second voltage detected by the even-numbered sampling to acquire
the voltage amplitude.
4. An apparatus according to claim 3, wherein the first voltage and
the second voltage are converted into insulation resistances,
respectively, and the difference between the converted resistances
is compared with a preset abnormality decision threshold value to
detect abnormality of the periodical waveform.
5. An apparatus according to claim 1, wherein the periodical
waveform is a square waveform.
6. A ground detection method for electric vehicle having a DC power
supply circuit which is electrically insulated from a body of
vehicle, a terminal of a coupling capacitor being connected to the
DC power supply circuit, comprising steps of: outputting a ground
detection signal comprising a periodical waveform through a
resistor to the other terminal of the coupling capacitor; detecting
a voltage of the other terminal of the coupling capacitor;
converting the detected voltage amplitude into an insulation
resistance on the basis of the relationship between a preset
voltage amplitude and a preset insulation resistance; and detecting
levels of insulation resistance deterioration of the DC power
supply circuit by comparing the converted insulation resistance
with a preset ground decision threshold value.
7. A method according to claim 6, wherein: the signal detecting
operation performs sampling of the voltage at a sampling period
which is a half the period of the periodical waveform to detect the
voltage; and the converting operation calculates a difference
between a first voltage detected by the odd-numbered sampling at
the sampling period and a second voltage detected by the
even-numbered sampling to acquire the voltage amplitude.
8. A ground detection apparatus for electric vehicle having a DC
power supply circuit which is electrically insulated from a body of
vehicle, comprising: coupling means which is connected to the DC
power supply circuit; output means for a ground detection signal
comprising a periodical waveform, the output means being connected
to one terminal of the coupling capacitor through a detection
resistor; signal detection means to detect a voltage amplitude of
one terminal of the coupling capacitor; conversion means to convert
the detected voltage amplitude into an insulation resistance on the
basis of the relationship between a preset voltage amplitude and a
preset insulation resistance; and level detection means to detect
levels of insulation resistance deterioration of the DC power
supply circuit by comparing the converted insulation resistance
with a preset ground decision threshold value.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a ground detection
apparatus for detecting the ground of a high-voltage DC power
supply mounted on an electric vehicle.
[0003] 2. Description of the Related Art
[0004] In an electric vehicle such as an electric automobile or a
hybrid electric automobile, in general, a high-voltage DC current
connected to a high-voltage battery is electrically insulated from
a vehicle electrical circuit connected to a body of vehicle. For
this reason, a ground detection apparatus is arranged for
generating a warning when dielectric breakdown occurs between the
high-voltage circuit and the body to decrease an insulation
resistance to generate ground.
[0005] An example of a ground detection apparatus for conventional
electric vehicle will be described below. In FIG. 1, reference
numeral 110 denotes a traveling drive circuit system, reference
numeral 51 denotes a battery group arranged as a high-voltage DC
power supply (e.g., 200 to 300 V) and electrically insulated from a
body B.
[0006] Reference numeral 52 denotes an inverter as a DC-AC
converter, reference numeral 53 denotes a three-phase AC motor for
vehicle traveling, reference numeral 54 denotes a plus bus serving
as a DC positive electrode feeder extending from the battery group
51 to the inverter 52, reference numeral 55 denotes a minus bus
serving as a DC negative electrode feeder extending from the
battery group 51 to the inverter 52, and reference numerals 56, 57,
and 58 denote an U-phase line, a V-phase line, and a W-phase line
which are AC feeders extending from the inverter 52 to the AC motor
53, respectively.
[0007] A conventional ground detection apparatus 100 shown in FIG.
1 is to detect the ground to the body B in the traveling drive
circuit system 110, and is constituted by an oscillation circuit 60
and a detection unit 80 for detecting a change in voltage
level.
[0008] A connection point P between the oscillation circuit 60 and
the detection unit 80 is connected to the plus bus 54 of the
battery group 51 of the traveling drive circuit system 110 through
a coupling capacitor 70A, and a DC component is isolated.
[0009] The oscillation circuit 60 comprises an oscillator 61 in
which a multi-vibrator is formed by an operational amplifier or the
like to generate a square wave having a predetermined frequency, an
impedance converter/buffer 62 which is arranged to prevent the
oscillation frequency of the oscillator 61 from being changed when
a load impedance changes in generation of ground in the traveling
drive circuit system 110, and a detection resistor 63 connected
between the output stage of the impedance converter 62 and the
coupling capacitor 70A. Reference numerals 65 and 66 denote
protecting diodes for protecting the impedance converter 62 from a
backward voltage or an overvoltage in generation of ground.
[0010] In the detection unit 80, a comparator 81 for comparing a
voltage level of the connection point P between the detection
resistor 63 and the coupling capacitor 70A at which an AC signal
output of the oscillation circuit 60 appears with a reference
voltage. The connection point P is connected to an inverted input
terminal. To a non-inverted input terminal of the comparator 81, a
reference voltage circuit is connected, where the reference voltage
thereof is set by partial-voltage resistors 88 and 89.
[0011] A smoothing circuit 86 in which a time constant is set by a
resistor 84 and a capacitor 85 is arranged at the output terminal
of the comparator 81. An output from the comparator 81 is inputted
to a non-inverted input terminal of a comparator 87 of the output
stage through the resistor 84 of the smoothing circuit 86.
[0012] The time constant of the smoothing circuit 86 is set such
that a smoothing voltage is lower than a reference voltage when an
output from the comparator 81 is a duty ratio of 50%, and the
smoothing voltage is higher than the reference voltage when an
output from the comparator 81 is a duty ratio of 100%.
[0013] A reference voltage circuit for setting a reference voltage
set by partial-voltage resistors 93 and 94 depending on the
smoothing voltage of the smoothing circuit 86 is connected to the
inverted input terminal of the comparator 87.
[0014] In the ground detection apparatus 100, reference numerals 91
and 92 denotes protecting diodes for protecting the comparator 81
from a backward voltage or an overvoltage in generation of
ground.
SUMMARY OF THE INVENTION
[0015] However, the conventional ground detection apparatus has the
following problems. The conventional ground detection apparatus has
the following configuration. That is, a voltage detected at a
ground detection point P by the comparators is compared with a
threshold voltage of a decrease in insulation resistance which is
determined by a circuit constant in advance to detect the
presence/absence of ground in the high-voltage DC power supply. For
this reason, in order to detect the decrease in insulation
resistance in several levels, comparators, the number of which is
equal to the number of levels of the decrease in insulation
resistance, for comparing threshold values of the decrease in
insulation resistance set in advance must be arranged. In order to
generate warnings depending on the several levels of the decrease
in insulation resistance, warning signal generation circuits, the
number of which is equal to the number of levels of the decrease in
insulation resistance, are required, the circuit configuration is
disadvantageously complicated.
[0016] When ground is generated in the battery group, and when the
peak value at the ground detection point P changes, the peak value
is converted into an effective value. The converted effective value
and the threshold value (or a reference voltage) of the decrease in
insulation resistance determined by a circuit constant in advance
are compared with each other by the comparator to detect insulation
resistance levels. For this reason, an error generated by the
effective value conversion is superposed on an error of the
reference voltage of the insulation resistance levels generated by
the circuit constant, so that levels of the decrease in insulation
resistance cannot be detected at a high precision
disadvantageously.
[0017] Therefore, according to the present invention, there is
provided a ground detection apparatus for vehicle in which the
circuit configuration can be simplified without increase in the
numbers of comparators, warning signal lines, and the like unlike
the related art, and the levels of the decrease in insulation
resistance of a DC voltage circuit with respect to a body can be
detected at a high precision in a plurality of stages. The present
invention provides ground detection apparatus for vehicle, which
can detect the presence/absence of an abnormal waveform of a ground
detection signal.
[0018] According to the first technical aspect of the present
invention, there is provided a ground detection apparatus for
electric vehicle including a DC power supply circuit which is
electrically insulated from a body and an AC circuit which is
driven by a DC voltage from the DC power supply circuit, wherein a
ground detection signal consisting of a periodical waveform is
supplied to the DC power supply circuit through a detection
resistor and a coupling capacitor, a voltage amplitude of a ground
detection point serving as a connection point between the detection
resistor and the coupling capacitor is detected, the detected
voltage amplitude is converted into an insulation resistance on the
basis of the relationship between a preset voltage amplitude and a
preset insulation resistance, and levels of insulation resistance
deterioration of the DC power supply circuit are detected by
comparing the converted insulation resistance with a preset ground
decision threshold value.
[0019] According to the second technical aspect of the present
invention, the ground detection apparatus, furthermore, performs
sampling of voltages at a sampling period which is 1/2 the period
of the periodical waveform to detect the voltages, and calculates a
difference between a first voltage detected by the odd-numbered
sampling in the sampling period and a second voltage detected by
the even-numbered sampling in the sampling period as the voltage
amplitude.
[0020] According to the third technical aspect of the present
invention, there is provided a ground detection method for electric
vehicle having a DC power supply circuit electrically insulated
from a body, the apparatus is coupled to the DC power supply
circuit through a coupling capacitor, includes the following steps.
More specifically, a ground detection signal consisting of a
periodical waveform is output to one terminal of the coupling
capacitor through a resistor, the voltage of one terminal of the
coupling capacitor is detected, on the basis of the relationship
between a preset voltage amplitude and an insulation resistance,
the detected voltage amplitude is converted into the insulation
resistance, and levels of insulation resistance deterioration of
the DC power supply circuit are detected by comparing the converted
insulation resistance with a preset ground decision threshold
value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a circuit diagram of a related ground detection
apparatus;
[0022] FIG. 2 is a diagram for explaining the ground detection
apparatus for vehicle and a traveling drive circuit system
according to one embodiment of the present invention;
[0023] FIG. 3 is timing chart showing a ground detection signal
(a), a sampling period (b), and the characteristics of A/D input
waveforms in normal (c) and abnormal states (d) in one embodiment
of the present invention;
[0024] FIG. 4 is an equivalent circuit diagram of a ground
detection apparatus when ground is generated on a positive
electrode side of a high-voltage DC power supply according to one
embodiment of the present invention;
[0025] FIG. 5 is an equivalent circuit diagram of a ground
detection apparatus when ground is generated on a negative
electrode side of a high-voltage DC power supply according to one
embodiment of the present invention;
[0026] FIG. 6 is a waveform chart of a ground detection signal
according to one embodiment of the present invention;
[0027] FIG. 7 is a flow chart showing the flow of a ground
detection operation in the ground detection apparatus according to
one embodiment of the present invention;
[0028] FIG. 8 is an equivalent circuit diagram for explaining a
ground detection operation in the ground detection apparatus
according to one embodiment of the present invention;
[0029] FIG. 9 is a chart explaining a voltage detection point of
time when a sampling point of time in a normal state is not
considered in the ground detection apparatus according to one
embodiment of the present invention;
[0030] FIG. 10 is a chart explaining a voltage detection point of
time when a sampling point of time in an abnormal state is not
considered in the ground detection apparatus according to one
embodiment of the present invention;
[0031] FIG. 11 is a chart explaining a voltage detection point of
time when a sampling point of time in a normal state is considered
in the ground detection apparatus according to one embodiment of
the present invention; and
[0032] FIG. 12 is a chart explaining a voltage detection point of
time when a sampling point of time in an abnormal state is
considered in the ground detection apparatus according to one
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0033] Embodiments of a ground detection potential of a vehicle
according to the present invention will be described below. FIG. 2
is a circuit diagram for explaining the configuration of a ground
detection apparatus 30 and a traveling drive circuit system 40 of
an electric vehicle according to one embodiment of the present
invention.
[0034] In FIG. 2, reference numeral 31 denotes a battery group
arranged as a high-voltage DC power supply (e.g., output voltage
VB=200 to 300 V) and electrically insulated from a body of vehicle
B.
[0035] Reference numeral 32 denotes an inverter for converting a DC
voltage into an AC voltage, reference numeral 33 denotes a
three-phase AC motor for vehicle traveling, reference numeral 34
denotes a plus bus serving as a DC positive electrode feeder
extending from the battery group 31 to the inverter 32, reference
numeral 35 denotes a minus bus serving as a DC negative electrode
feeder extending from the battery group 31 to the inverter 32,
reference numerals 36, 37, and 38 denote a U-phase line, a V-phase
line, respectively.
[0036] The ground detection apparatus 30 according to the
embodiment has a microcomputer 1 incorporating CPU 26, RAM 25, ROM
27, and a square wave generator 14 for outputting a ground
detection signal of a square wave having a period 2T, a detection
resistor 3 connected to the microcomputer 1, a coupling capacitor 4
to which a connection point between the coupling capacitor 4 and
the detection resistor 3 is connected as a ground detection point
A, an A/D (analog/digital) input unit 11, arranged in the
microcomputer 1 and connected to the ground detection point A by a
connection line 5, for performing repeated sampling voltages of the
ground detection point A every sampling period T to measure the
voltages, one pair of zener diodes 22 connected between a resistor
21 connected between the A/D converter 11 and a ground detection
point A, the A/D converter 11, and the ground, and a warning signal
line 6 which is guided from a warning signal output unit 12
arranged in the microcomputer 1 and which is connected to an output
terminal 13. The output terminal 13 is connected to an attention
lamp 15 and a warning lamp 16.
[0037] The other connection terminal of the coupling capacitor 4 is
connected to the plus bus 34 of the high-voltage DC power supply
31.
[0038] In the microcomputer 1 described above, voltage
amplitude-insulation resistance corresponding data (to be described
later) representing the relationship between a voltage amplitude
and an insulation resistance, ground decision threshold values of a
plurality of levels for deciding ground of the high-voltage DC
power supply 31, and an abnormality decision threshold value
R.sub.ck for deciding an abnormal waveform of the ground detection
signal of the square wave are set and stored in a memory (ROM
27).
[0039] As shown in FIG. 3, the ground detection signal constituting
a square waveform, a sampling period T obtained by the A/D
converter 11, and the relationship between an input voltage to the
A/D converter 11 in a normal state and an input voltage to the A/D
converter 11 in a state of insulation resistance deterioration
caused by ground generation in the high-voltage DC power supply 31
will be described below.
[0040] The ground detection signal of the square wave forms a
waveform constituted by one period of 2T comprising of, as one T an
odd-numbered term Ti (i=2n-1) having a voltage E(V) and as the
other T an even-numbered term Tj (j=2n) having a voltage of 0 V. In
this case, reference numeral n denotes a positive integer (1, 2, 3,
. . .).
[0041] The A/D converter 11, as shown in FIG. 3(b), sequentially
performs repeated sampling of voltages of the ground detection
point A at time intervals from the halfway point of the period T
with the odd-numbered term Ti to the halfway point of the period T
with the even-numbered term Tj, to be equivalent to a period T on
the basis of control of the microcomputer 1 and the sampled data is
temporarily stored in a storage such as RAM 25.
[0042] The input voltage to the A/D converter 11 in the normal
state is a voltage amplitude Va having a waveform similar to the
waveform (FIG. 3(a)) of the ground detection signal of the square
wave as shown in FIG. 3(c) because an insulation resistance is
deteriorated by ground generation in the high-voltage DC power
supply 31.
[0043] On the other hand, when ground is generated in the
high-voltage DC power supply 31, a voltage amplitude Va' which is
an input voltage of the A/D converter 11 as shown in FIG. 3(d), is
smaller than a value Va obtained in a normal state (Va>Va')
because the voltage of the ground detection point A changes by a
partial voltage of the detection resistor 3 and an insulation
resistor 20 (insulation resistance R.sub.L) between the detection
resistor 3 and the ground.
[0044] A case in which the insulation resistance is deteriorated by
generation of ground on the anode side of the high-voltage DC power
supply 31 will be described below with reference to the equivalent
circuit diagram of the ground detection apparatus 30 shown in FIG.
4 and the waveform chart of the ground detection signal shown in
FIG. 6.
[0045] In the equivalent circuit shown in FIG. 4, a current value
of a ground detection signal is represented by i(t), the resistance
of the detection resistor 3 by R.sub.0, the insulation resistance
of the insulation resistor 20 by R.sub.L, the capacitance of the
coupling capacitor 4, by C and the voltage of a ground detection
signal output from the square wave generator 14 by E,
respectively.
[0046] A voltage Va1 (2n-1) of the ground detection signal
subjected to sampling in a section of the odd-numbered term
Ti{0.ltoreq.t.ltoreq.T} is calculated. In this case, as is apparent
from FIG. 4, the following Equation (1) is obtained. 1 1 C i t + (
R 0 + R L ) i = E ( eq . 1 )
[0047] Equation (1) is solved by using Laplace transform, the
current value i(t) of the ground detection signal is given by the
following Equation (2). 2 i ( t ) = E R 0 + R L t C ( R 0 + R L ) (
eq . 2 )
[0048] Therefore, a voltage Va.sub.1(2n-1) of a ground detection
signal having a square waveform subjected to sampling in a section
of the odd-numbered term Ti{0.ltoreq.t.ltoreq.T} can be calculated
for time duration of 0.ltoreq.t.ltoreq.T by Equation (3). 3 Va 1 (
2 n - 1 ) = E - R 0 i ( t ) = E ( 1 - R 0 R 0 + R L t C ( R 0 + R L
) ) ( eq . 3 )
[0049] In this manner, voltage amplitude-insulation resistance
relationship in the odd-numbered term Ti can be obtained.
[0050] A voltage Va.sub.2(2n) subjected to sampling in a section of
the even-numbered term Tj is calculated for time variation of
T.ltoreq.t.ltoreq.2T. In this case, with respect to a voltage
initial value Va.sub.2(t=T) at an initial point of time in a
section of the even-numbered term Tj, a charge accumulated in a
coupling capacitor is calculated by using Equation (2), so that
Equation (4) can be obtained with respect to a voltage Vc(t=T)
generated across both the ends of the coupling capacitor. 4 V C ( t
= T ) = 1 C [ i t ] t = T = E ( 1 - T C ( R 0 + R L ) ) ( eq . 4
)
[0051] Therefore, according to Equation (1), i
(t=T)=-Vc(t=T)/(R.sub.0+R.s- ub.L) is satisfied, and the current
value i(t) of the ground detection signal can be calculated by
Equation (5). 5 i ( t ) = - E R 0 + R L ( 1 - T C ( R 0 + R L ) ) t
- T C ( R 0 - R L ) ( eq . 5 )
[0052] Therefore, a voltage Va.sub.2(2n) subjected to sampling in a
section of the even-numbered term Tj can be calculated for duration
of T.ltoreq.t.ltoreq.2T by Equation (6). 6 Va 2 ( 2 n ) = 0 - R 0 i
( t ) = R 0 R 0 + R L E ( 1 - T C ( R 0 + R L ) ) t - T C ( R 0 + R
L ) ( eq . 6 )
[0053] In this manner, voltage amplitude-insulation resistance
relationship in the even-numbered term Tj{T.ltoreq.t.ltoreq.2T} can
be obtained.
[0054] A case in which an insulation resistance is deteriorated by
generation of ground on the ground side of the high-voltage DC
power supply 31 will be described with reference to the equivalent
circuit diagram in FIG. 5 and the waveform chart in FIG. 6.
[0055] A voltage Va.sub.1'(2n-1) subjected to sampling in a section
of the odd-numbered term Ti{0.ltoreq.t.ltoreq.T} is calculated. In
this case, as shown in FIG. 5, when it is considered that E=0
represents a stationary state while t.ltoreq.0, a coupling
capacitor C has an impedance which is considerably larger than the
resistances R.sub.0 and R'.sub.L. For this reason, a voltage
V.sub.B may be almost entirely applied to the coupling capacitor C,
therefore, Equation (7) is satisfied. 7 1 C i t + ( R 0 + R L ' ) i
= E - V B ( eq . 7 )
[0056] In Equation (7), reference symbol V.sub.B denotes an initial
(t=0) voltage value of the coupling capacitor 4. At this time,
charges +V.sub.BC and -V.sub.BC are accumulated in both the poles
of the coupling capacitor C, respectively. Equation (7) is solved
by using Laplace transform with respect to the current value i(t)
of a ground detection signal, Equation (8) can be obtained. 8 i ( t
) = E R 0 + R L ' t C ( R 0 + R L ' ) ( eq . 8 )
[0057] Therefore, a voltage Va.sub.1'(2n-1) subjected to sampling
in a section of the odd-numbered term Ti for duration of
0.ltoreq.t.ltoreq.T can be calculated by Equation (9) which is the
same as Equation (3). 9 Va 1 ( 2 n - 1 ) ' = E - R 0 i ( t ) = E (
1 - R 0 R 0 + R L ' t C ( R 0 + R L ' ) ) ( eq . 9 )
[0058] A voltage Va.sub.2'(2n) subjected to sampling in a section
of the even-numbered term Tj for {T.ltoreq.t.ltoreq.2T} is
calculated. In this case, Equation (10) is established with respect
to an initial point of time in the section of the even-numbered
term Tj for duration of T.ltoreq.t.ltoreq.2T. 10 1 C i t + ( R 0 +
R L ' ) i = 0 - V B ( eq . 10 )
[0059] When Equation (10) is solved by using Laplace transform with
respect to the current value i(t) of the ground detection signal,
Equation (11) can be obtained. 11 i ( t ) = - E R 0 + R L ' ( 1 - e
- T C ( R 0 + R L ' ) ) e - t - T C ( R 0 + R L ' ) ( eq . 11 )
[0060] Therefore, a voltage Va.sub.2'(2n) subjected to sampling in
a section of the even-numbered term Tj{T.ltoreq.t.ltoreq.2T} can be
calculated by Equation (12) which is the same form as Equation (6).
12 V a 2 ( 2 n ) ' = 0 - R 0 i ( t ) = R 0 R 0 + R L ' E ( 1 - e -
T C ( R 0 + R L ' ) ) e - t - T C ( R 0 + R L ' ) ( eq . 12 )
[0061] Procedure for detecting deterioration of the insulation
resistor 20 (insulation resistance R.sub.L) of the high-voltage DC
power supply 31 on the basis of the voltages Va.sub.1 and Va.sub.2
(or the voltages Va.sub.1' and Va.sub.2') obtained as described
above will be described below.
[0062] (A) Case in which deterioration of insulation resistance
does not occur in the high-voltage DC power supply 31
[0063] In this case, the insulation resistance R.sub.L of the
insulation resistor 20 is infinite, and, in a section in which a
voltage output from the square wave generator 14 is E (V), Equation
(13) is established according to Equation (3) with respect to the
voltage Va.sub.1. 13 Va 1 = E ( 1 - R 0 R 0 + R L e - t C ( R 0 + R
L ) ) ( eq . 13 )
[0064] In this case, since the insulation resistance R.sub.L is
infinite, it can be estimated such that R.sub.0/R.sub.L<<1,
and the exponential term of the second term in parentheses of the
right side can be estimated by Equation (14). 14 exp ( - t C ( R 0
+ R L ) ) 1 ( eq . 14 )
[0065] Therefore, in this case, a voltage Va.sub.1 of the ground
detection point A can be expressed by Equation (15).
Va.sub.1.congruent.E(1-0.times.1)=E (eq 15)
[0066] On the other hand, in a section in which a voltage output
from the square wave generator 14 is 0 (V), a voltage Va.sub.2 of
the ground detection point A can be expressed by Equation (16)
according to Equation (6). 15 V a 2 = R 0 R 0 + R L E ( 1 - e - T C
( R 0 + R L ) ) e - t - T C ( R 0 + R L ) ( eq . 16 )
[0067] In this case, since the insulation resistance R.sub.L is
infinite, Equation (17) is satisfied with respect to the respective
elements of the right hand of Equation (16). 16 Va 2 = 0 ( T C ( R
0 + R L ) 1 ) ( eq . 17 )
[0068] Therefore, a voltage (absolute-value voltage) Va of the
ground detection point at this time can be expressed by Equation
(18) on the basis of Equations (15) and (17).
Va=Va.sub.1-Va.sub.2=E-0=E(V) (eq. 18)
[0069] (B) Case in which deterioration of insulation resistance
occurs in high-voltage DC power supply 31
[0070] In this case, an insulation resistance R.sub.L' of a
insulation resistor 20' satisfies R.sub.L'>0, the voltage Va of
the ground detection point A establishes Equation (19) according to
Equation (9) and Equation (12) with respect to a section in which a
voltage output from the square wave generator 14 is E (V) and a
section in which the voltage output from the square wave generator
14 is 0 (V). Here, 0.ltoreq.t.sub.1.ltoreq.T and
T.ltoreq.t.sub.2.ltoreq.2T are satisfied. 17 V a = Va 1 ' - Va 2 '
= E { ( 1 - R 0 R 0 + R L ' e - t 1 C ( R 0 + R L ' ) ) - R 0 R 0 +
R L ' ( 1 - e - T C ( R 0 + R L ' ) ) e - t 2 - T C ( R 0 + R L ' )
} ( eq . 19 )
[0071] When sampling is performed at equal intervals T, t.sub.1 and
t.sub.2 can be given as t.sub.1=0+t and t.sub.2=T+t. For this
reason, Equation (19') can be obtained. 18 Va = E { 1 - 2 R 0 R 0 +
R L ' e - t C ( R 0 + R L ' ) + R 0 R 0 + R L ' e - T + t C ( R 0 +
R L ' ) } ( eq . 19 ' )
[0072] (C) Case in which high-voltage DC power supply 31 is
short-circuited to body B
[0073] In this case, the insulation resistance R.sub.L of the
insulation resistor 20 is given by R.sub.L=0. At this time,
Equation (20) is established with respect to voltage Va. 19 Va = Va
1 ' - Va 2 ' = E { ( 1 - e - t 1 CR 0 ) - ( 1 - e - T CR 0 ) e - t
2 - T CR 0 } ( eq . 20 )
[0074] Therefore, Equation (20') can be obtained in the same manner
as Equation (19'). 20 V a = E { 1 - 2 e - t CR 0 + e - T + t CR 0 }
( eq . 20 ' )
[0075] Ground Detection Operation
[0076] The flow of a ground detection operation of the high-voltage
DC power supply 31 by the ground detection apparatus 30 according
to the embodiment will be described below with reference to the
flow chart shown in FIG. 7.
[0077] When the ground detection operation by the ground detection
apparatus 30 is started (Step ST1), the square wave generator 14
oscillates a square wave of 0-E (V) (Step ST2) and supplies a
ground detection signal to the high-voltage DC power supply 31
through the detection resistor 3 and the coupling capacitor 4.
[0078] In this manner, the microcomputer 1 performs sampling of a
voltage Va of the ground detection point A at a timing synchronized
with the period of the ground detection signal from the A/D
converter 11 connected to the ground detection point A. More
specifically, sampling is performed to voltage amplitude Va(2n-1)
during the odd-numbered term and voltage amplitude Va(2n) during
the even-numbered term (Step ST3).
[0079] The microcomputer 1 converts the voltage amplitude Va(2n-1)
into an insulation resistance R.sub.LH for detecting an abnormal
waveform on the basis of voltage amplitude voltage-insulation
resistance corresponding data representing the relationship between
a preset voltage amplitude and a preset insulation resistance (Step
ST4).
[0080] More specifically, on the basis of a characteristic curve of
voltage amplitude-insulation resistance relationship obtained by a
relational expression indicated by Equation (3) (or Equation (9)),
an optimized insulation resistance R.sub.L is calculated by
substituting the voltage amplitude Va(2n-1) for the characteristic
curve, and the resistance is represented by R.sub.LH (Step
ST4).
[0081] Similarly, by substituting the voltage amplitude Va(2n) for
the characteristic curve of the voltage amplitude-insulation
resistance corresponding data obtained by the relational expression
shown in Equation (6) (or Equation (12)), an optimized insulation
resistance R.sub.L is calculated, and the resistance is represented
by R.sub.LL (Step ST5).
[0082] The microcomputer 1 compares the absolute value of the
difference between the converted insulation value R.sub.LH for
detecting an abnormal waveform and the resistance R.sub.LL with the
abnormality decision threshold value R.sub.CK (Step ST6). When the
absolute value is larger than the abnormality decision threshold
value R.sub.CK (NO in step ST6), it is decided that a ground
detection signal waveform output from the microcomputer 1 has
abnormality (Step ST11).
[0083] On the other hand, when the absolute value is smaller than
the abnormality decision threshold value R.sub.CK (YES in step
ST6), on the basis of the voltage amplitude Va(2n-1) and the
voltage amplitude Va(2n) which are calculated in steps ST4 and ST5,
the microcomputer 1 calculates an absolute-value voltage (voltage
amplitude) Va of the difference between these amplitudes (Step
ST7). In addition, the voltage Va is converted into the insulation
resistance R.sub.L on the basis of voltage amplitude--insulation
resistance corresponding data representing the relationship a
preset voltage amplitude and a preset insulation resistance (Step
ST8).
[0084] More specifically, a characteristic curve representing the
relationship between the insulation resistance R.sub.L and the
absolute-value voltage Va obtained by Equation (19) described above
is formed, and the absolute-value voltage Va calculated in step ST7
is substituted for the characteristic curve, so that an optimized
insulation resistance R.sub.L is calculated. It is apparent that
another parameter fitting can be applied.
[0085] The microcomputer 1 compares the insulation resistance
R.sub.L with a preset ground decision threshold value for ground
decision of the high-voltage DC power supply 31 (Step ST9). When
the insulation resistance R.sub.L decreases to the level of the
ground decision threshold value (YES in step ST9), an insulation
resistance decrease warning signal is sent to the terminal 13
through the warning signal line 6 (Step ST10). When the insulation
resistance R.sub.L does not decrease to the level of the ground
decision threshold value (NO in step ST9), the processes started
from step ST3 are repeated. In this manner, when ground is
generated in the high-voltage DC power supply 31, the ground can be
immediately detected.
[0086] As described above, in the ground detection apparatus 30,
sampling is performed to acquire a voltage generated at the ground
detection point A in a sampling period T which is 1/2 the period 2T
of a ground detection signal (square waveform signal). On the basis
of the value of the difference between a voltage amplitude obtained
by the odd-numbered sampling and a voltage amplitude obtained by
the even-numbered sampling, the insulation resistance R.sub.L of
the high-voltage DC power supply 31 is obtained. Therefore, since
voltage amplitudes of the ground detection point are detected at
predetermined intervals, the detection corresponds to that t is
fixed in Equation (19'). For this reason, the voltage amplitude can
be correctly specified. Therefore, according to the present
invention, there can be provided a ground detection apparatus for
vehicle which can detect the level of insulation resistance
deterioration of the DC power supply circuit at a higher
precision.
[0087] The insulation resistance R.sub.LH is calculated on the
basis of the voltage amplitude Va(2n-1) obtained at the
odd-numbered sampling, and the insulation resistance R.sub.LL is
calculated on the voltage amplifier Va(2n) obtained at the
even-numbered sampling. Since, by using the difference between the
insulation resistance R.sub.LH and the insulation resistance
R.sub.LL, it can be detected whether abnormality occurs in the
ground detection signal or not. For this reason, more reliable
ground detection can be performed.
[0088] In addition, since the apparatus is designed such that a
ground detection signal and a sampling pulse are outputted by using
the microcomputer 1, the sampling pulse can be easily synchronized
with the ground detection signal. Since a plurality of threshold
values of a warning signal can be set, the number of warning signal
lines can be reduced in comparison with the related art.
[0089] A concrete example of a ground detection operation of the
high-voltage DC power supply 31 by the ground detection apparatus
30 according to the embodiment will be described below with
reference to FIG. 8.
[0090] In the equivalent circuit shown in FIG. 8, it is assumed
that a resistance of the detection resistor 3 is represented by
R.sub.0, that an insulation resistance of the insulation resistor
20 is given by R.sub.L=43 k.OMEGA., and that the capacitance C of
the coupling capacitor 4=2.2 .mu.F. It is assumed that the voltage
E of the square wave generator 14 has a square waveform of 100 Hz,
is 5 (V) in a section of the odd-numbered term
Ti{0.ltoreq.t.ltoreq.T}, and is 0 (V) in a section of the
odd-numbered term Tj{T.ltoreq.t.ltoreq.2T}.
[0091] A ground decision threshold value CA of an attention level
is defined by 4.3 k.OMEGA.<R.sub.L <3 k.OMEGA., and a ground
decision threshold value FA of a warning level is defined by
R.sub.L.ltoreq.4.3 k.OMEGA.. In this state, the following
description is performed.
[0092] As shown in FIG. 9, when actual sampling time is not
considered, the insulation resistance R.sub.L of the insulation
resistance of the high-voltage DC power supply 31 is R.sub.L=30
k.OMEGA. which is equal to the upper limit of the ground decision
threshold value CA of the attention level, an absolute-value
voltage Va which is the difference between a voltage amplitude Va1
and a voltage amplitude Va.sub.2 which are calculated on the basis
of Equation (3) and Equation (6) described above is 1.85 (V).
[0093] As shown in FIG. 10, when the actual sampling time is not
considered, when the insulation resistance R.sub.L of the
insulation resistance of the high-voltage DC power supply 31
decreases to 4.3 k.OMEGA. which is the ground decision threshold
value FA of the warning level, the absolute-value voltage Va which
is the difference between the voltage amplitude Va.sub.1 and the
voltage amplitude Va.sub.2 which are calculated on the basis of
Equation (3) and Equation (6) described above is 1.85 (V).
[0094] As shown in FIGS. 11 and 12, a case in which the actual
sampling time is considered will be described below. In this case,
the insulation resistance R.sub.L of the insulation resistance of
the high-voltage DC power supply 31 is R.sub.L=30 k.OMEGA. which is
equal to the upper limit of the ground decision threshold value CA
of the attention level is 2.11 (V). The voltage amplitude Va.sub.2
is 0.08 (V). Therefore, the absolute-value voltage Va which is the
difference between the voltage amplitude Va1 and the voltage
amplitude Va.sub.2 is 2.03 (V).
[0095] When the actual sampling time is considered, and when the
insulation resistance R.sub.L of the insulation resistance of the
high-voltage DC power supply 31 decreases to 4.3 k.OMEGA. which is
equal to the ground decision threshold value FA of the warning
level, the voltage amplitude Va.sub.1 is 0.55 (V). In addition, the
voltage amplitude Va.sub.2 is 0.21 (V).
[0096] Therefore, the absolute-value voltage Va which is the
difference between the voltage amplitude Va.sub.1 and the voltage
amplitude Va.sub.2 is 0.34 (V).
[0097] From the above results, when the absolute-value voltage
Va.sub.0 to be calculated is 2.0 (V) or less, a signal of an
attention level is output from the warning signal line 6 to turn
on, e.g., the attention lamp 15. When the absolute-value voltage
Va.sub.0 is 0.5 (V) or less, a signal of a warning level is output
from the alarm signal line 6 to turn on the alarm lamp 16 and
attention or warning is displayed.
[0098] This application claims benefit of priority under 35USC
.sctn.119 to Japanese Patent Applications No. 2001-004120, filed on
Jan. 11, 2001, the entire contents of which are incorporated by
reference herein. Although the invention has been described above
by reference to certain embodiments of the invention, the invention
is not limited to the embodiments described above. Modifications
and variations of the embodiments described above will occur to
those skilled in the art, in light of the teachings. The scope of
the invention is defined with reference to the following
claims.
* * * * *